1. Field of the Invention
The invention relates to output drivers, and more particularly, to multifunctional output drivers capable of transmitting signals of different specifications in different modes.
2. Description of the Related Art
Low voltage differential signaling, or LVDS, is an electrical signaling system that can run at very high speeds over twisted-pair copper cables. LVDS is a differential signaling system, which means that it transmits two different voltages which are compared at the receiver. LVDS uses the difference in voltage between the two wires to encode information. The transmitter injects a small current, nominally 3.5 mA, into one wire or the other, depending on the logic level to be sent. The current passes through a resistor of about 100 to 120Ω at the receiving end, and then returns in the opposite direction along the other wire. From Ohm's law, the voltage difference across the resistor is therefore about 350 mV. The receiver senses the polarity of this voltage to determine the logic level. This type of signaling is called a current loop. The small amplitude of the signal and the tight electric- and magnetic-field coupling between the two wires reduces the amount of radiated electromagnetic noise.
Current-mode logic (CML) circuits are commonly used in applications where maximum operational speed is desired. CML circuits use differential low-voltage signaling and have constant power consumption. A CML gate consists of a dc current source, a differential load and a switching network, composed of either MOSFETs or bipolar transistors, which connect the current source to the differential load. The transmission is point-to-point, unidirectional and is usually terminated at the destination with 50Ω resistors to Vcc on both links.
Because different display panels require different transmission interfaces, there is a need for a multifunctional output driver capable of transmitting signals of different interfaces in different modes in order to reduce costs and power consumption.